Authored by Justin R. Miller

update changelog for 1.5.1

Changelog
---------
### 1.5.1
#### January 28, 2015
- Deprecated `+[RMConfiguration configuration]` in favor of the Swift-friendly and better-looking `+[RMConfiguration sharedInstance]`.
- Fixed a bug in the docs removal script.
- Documentation improvements.
### 1.5.0
#### January 16, 2015
... ...